Method for controlling suspension apparatus for vehicle

Abstract

An improved method for controlling a suspension apparatus for a vehicle which is capable of enhancing a boarding-on feeling and a running stability by increasing a boarding-on feeling and the road surface contact force of wheels based on the size of a road surface input and a control logic which is variable in accordance with a frequency. The method includes the steps of obtaining a displacement value by passing an acceleration value measured by a vehicle vertical acceleration sensor through an integration unit having the following Equation (1); and computing a predetermined road surface signal by using the acceleration and displacement value as shown in Equation (2); ##EQU1## where, ξ 1 and w 1 are coefficients used for determining the coefficient of the filter used in the integration. r(t)=d.sub.s (t)+c×a.sub.s (t) (2)

What is claimed is: 
     
       1. A method for controlling a boarding-on feeling in a suspension apparatus for a vehicle comprising the steps of: obtaining a displacement value d(S) by integrating an acceleration value measured by a vehicle vertical acceleration sensor through a plurality of integration units having the following Equation (1): ##EQU9## where, v(S) is a vertical velocity value, a(S) is a vertical acceleration value, S is a Laplace changer, ε 1  is a coefficient of attenuation, and ω 1  is a passing frequency of low pass filter; and   computing a road surface signal by using the acceleration and displacement value as shown in the following Equation (2) wherein the results of said following Equation (2) are used to control said boarding-on feeling in a suspension apparatus in a vehicle;   r(t)=d.sub.s (t)+c×a.sub.s (t)                       (2)       where, r(t) is a road surface computation value in time domain, ds(t) is a vertical displacement value, c is a coefficient, and as(t) is a vertical acceleration value.   
     
     
       2. The method of claim 1, further comprising the steps of: computing a signal corresponding to a vehicle resonant region by passing the road surface signal through high and low pass filters based on the following Equations (3) and (4): ##EQU10## where, r.sub.η (S) is a low frequency value of a road surface and r(S) is a road surface computation value in frequency domain, ##EQU11## where r12(S) is a high frequency value of a road surface; and computing a representative value corresponding to a low frequency of a road surface by passing the signal representative of vehicle resonance and an absolute value obtained in the following Equation (5) through a low frequency pass filter: ##EQU12## where, r 1 (s) is a power computation result value of a vehicle resonant region and TS is a time constant. 
     
     
       3. The method of claim 2, further comprising the steps of: computing a signal corresponding to a vehicle resonant region by passing the road surface signal through a high frequency pass filter as shown in the following Equation (6): ##EQU13## where, r h1  (S) is a passing signal of the high frequency filter and r(S) is a road surface computation value in frequency domain; and   computing a representative value corresponding to a high frequency of a road service by passing the signal representative of vehicle resonance and an absolute value obeyed in the following Equation (7) through a low frequency pass filter: ##EQU14## where r h  (S) is a power computation resultant value of a vehicle resonant region.   
     
     
       4. The method of claim 3, further comprising the steps of: obtaining a ratio by dividing the computed high frequency representative value and the computed low frequency representative value of a road surface as shown in the following Equation (8): ##EQU15## where ωc(t) is a frequency ratio of a road surface, r 1  (t) is low frequency value of a road surface in time domain and r.sub.η (t) is a computation resultant value of a vehicle resonant region in time domain; and   computing a difference of the frequencies of a road surface on which a vehicle runs.   
     
     
       5. The method of claim 4, further comprising the steps of: forming a two-dimensional map based on two control variables with respect to a high frequency representative value of a road surface and a frequency ratio of a road surface; and   increasing a damping force when a frequency value is increased and increasing the same when a frequency ratio of a road surface is increased.   
     
     
       6. The method of claim 1, further comprising the steps of: computing a signal corresponding to a vehicle resonant region by passing the road surface signal through a high frequency pass filter as shown in the following Equation (6): ##EQU16## where, r h1  (S) is a passing signal of the high frequency filter and r(S) is a road surface computation value in frequency domain; and   computing a representative value corresponding to a high frequency of a road surface by passing the signal representative of vehicle resonance and an absolute value obtained in the following Equation (7) through a low frequency pass filter: ##EQU17## where r h  (S) is a power computation resultant value of a vehicle resonant region.   
     
     
       7. The method of claim 6, further comprising the steps of: obtaining a ratio by dividing a high frequency representative value and a low frequency representative value of a road surface as shown in the following Equation (8): ##EQU18## and computing a difference of the frequencies of a road surface on which a vehicle runs.   
     
     
       8. The method of claim 6, further comprising the steps of: forming a two-dimensional map based on two control variables with respect to the high frequency representative value of a road surface and the frequency ratio of a road surface; and   increasing a damping force when any one of a frequency value is increased and a frequency ratio of a road surface is increased.